Mobile wireless communications often rely on Base Station Antennas having phased arrays of multiple radiating elements to achieve desired beam shape, angle, and polarization. For example, a common Base Station Antenna may have a single column of dual-polarized radiating elements. This would be considered a two-port antenna. Other antennas may have additional arrays of radiating elements for additional bands to increase capacity. See, for example, U.S. Pat. No. 7,659,859 which is incorporated by reference.
Also, in mobile wireless systems there are two different radio frequency paths that may be optimized. The first is the Radio Frequency (“RF”) path from the Base Station Antenna (BSA) to the user equipment (UE), and is referred to as the “downlink” path. The second is the RF path from the UE back to the BSA, and is referred to as the “uplink” path. For LTE applications, the downlink must typically support much higher data rates than the uplink. The reason for this is customer demand for features like streaming video and live TV.
The 3rd Generation Partnership Project (3GPP) Standards Body has defined Long Term Evolution (LTE) as the latest modulation scheme that the cellular industry can use, with the promise of much faster data speeds compared to legacy systems. In order to accomplish this, 3GPP has introduced a number of new concepts that are just beginning to be implemented. For example, with the E-UTRAN LTE 3GPP specifications, Multiple Input, Multiple Output (MIMO) transmission modes are defined.
MIMO transmission modes may be used in different ways. In one mode, transmit diversity may be achieved. In this example, each antenna array transmits the same information, and an increase in received power may be achieved. In other examples, different antenna arrays may transmit different streams of information. In this example, throughput is increased.
There are various MIMO configurations, typically delineated by the number of transmit antennas and by the number of receive antennas. For example, where a Base Station Antenna has four columns available for transmitting, and the User Equipment (UE) has two antennas for reception, the path from the path from the BSA to the UE is said to have 4×2 MIMO. One example of an antenna family suited to 4×N transmit MIMO is the CommScope SBNHH family, which has two columns of cross-polarized radiating elements for high-band signals, resulting in a four-port antenna for high band signals. The radiating elements are wide-band elements, configured to operate in a band of 1710-2360 MHz. The columns are spaced apart one wavelength or less.